how to give options in sub select type in meta box

how it possible ??
http://prntscr.com/8b4cyh

this is my meta box code

<?php
/**
* Initialize the custom Meta Boxes.
*/
add_action( ‘admin_init’, ‘diva_meta_boxes’ );

/**
* Meta Boxes demo code.
*
* You can find all the available option types in demo-theme-options.php.
*
* @return void
* @since 2.0
*/
function diva_meta_boxes() {

/**
* Create a custom meta boxes array that we pass to
* the OptionTree Meta Box API Class.
*/
$diva_meta_boxes = array(
‘id’ => ‘diva_select_layout’,
‘title’ => __( ‘Select The Layout’, ‘theme-text-domain’ ),
‘desc’ => ”,
‘pages’ => array( ‘page’, ‘all_goals’ ),
‘context’ => ‘normal’,
‘priority’ => ‘high’,
‘fields’ => array(
array(

‘id’ => ‘select_layout_diva’,
‘type’ => ‘select’,
‘desc’ => __( ‘<b>Please choose the layout of this page.</b>’, ‘theme-text-domain’ ),

‘choices’ => array(
array(
‘value’ => ”,
‘label’ => ‘– Choose One –‘
),
array(
‘value’ => ‘front’,
‘label’ => ‘Front Page’
),
array(
‘value’ => ‘blog’,
‘label’ => ‘Blog’
)
)
)
)
);

/**
* Register our meta boxes using the
* ot_register_meta_box() function.
*/

ot_register_meta_box( $diva_meta_boxes );

}

https://wordpress.org/plugins/option-tree/